1. Field of the Invention
This invention pertains to nuclear reactor internals, and more particularly to an internals arrangement whereby a core is made accessible by removal of the reactor control rods and the upper core support as a single unit.
2. Description of the Prior Art
In a commercial nuclear reactor, heat, from which electricity is generated, is produced by fissioning of a fissile material, such as enriched uranium. This fissile material, or nuclear fuel, is typically contained within a core made up of a plurality of fuel elements, coextensively arranged in a spaced parallel array. Movable control rods are dispersed throughout the core to control the fission process. The control rods often comprise a plurality of elongated rods containing neutron absorbing materials, for example silver, indium and cadmium which fit in openings among the fuel elements so as to be guided thereby during movement into and out of the core. Inserting a control rod into the core adds more absorber material and hence, decreases the nuclear reaction; conversely, withdrawing a control rod removes absorber material and hence, increases the nuclear reaction and thereby, the power output. The nuclear core and the control rods are positioned within and supported by a reactor vessel.
The heat produced by the nuclear reaction is removed by flowing a reactor coolant through the nuclear core. This heat is then transferred from the reactor coolant to a fluid in another flow system where it is converted into steam which is used to drive steam turbine-electrical generator apparatus. The flow of the reactor coolant through the nuclear core produces large structural loads on the core; therefore, a core support system is provided which is typically both strong and rigid to carry these loads and to assure safety of reactor operation. The core support system, or as it is sometimes called the nulcear reactor industry, "the reactor internals" serve to: fixedly position and support the fuel assemblies comprising the nuclear core, guide and support the nuclear reactor control rods, and direct the flow of reactor coolant through the nuclear core and the reactor vessel within which the core is contained.
In the prior art, primarily because of the structural and safety functions performed by the reactor internals, the various components of the reactor internals are assembled to each other in such a way as to assure their integrity during reactor operation. Therefore, in order to disassemble the reactor internals, each component or subassembly must be individually disconnected from another component or subassembly in sequential fashion. It is obvious then that such a disassembly procedure involves a significant length of time and a significant expenditure of manpower in order to expose the nuclear core for purposes of refueling the core. Moreover, the reactor downtime resulting from the refueling operation, and therefore, the period of time when the reactor is unavailable for the production of electricity, is directly dependent upon the time required to disassemble and reassemble the reactor internals during refueling of the core.